1. Field of the Invention
The invention relates to a method for analyzing and evaluating measured values of an open test system where, during a test run, a test piece is monitored by at least one signal channel which sends a signal to an evaluation unit for further processing whereby at least one plausibility node is coupled with at least one signal channel.
2. The Prior Art
Testing and measuring systems for research and development, in particular in motor vehicle technology and for the engine and drive train of a vehicle, for example, have today, by necessity, become themselves almost unmanageably complex and highly sophisticated products. In relatively short test periods, enormous quantities of test data occur and are recorded or stored. User-friendly software tools make even extensive evaluations of measured data possible, which are used for evaluating test runs and the test piece, and in particular for the optimization of its desired performance criteria. Furthermore, there are new types of software packages for the automatic carrying out of test runs and for the automatic determination of optimum operating points of the test piece, which significantly contribute to the reduction in development time and to an improvement of the quality of development results and the products themselves.
For such test runs, test stands (but also mobile measuring equipment or devices) are often in operation for hours and the development result depends on whether the entire system has worked without errors through-out this long test period. The user has to be able to rely on the fact that the measured and test data are significant and usable. A critical error, e.g. a changed sensitivity of a sensor, can cause not only enormous costs (test stand costs, equipment and consumables costs, test piece costs, personnel costs, etc.), but can also, most of all, have the effect of a delay in the development process, which is associated with extreme costs and competitive disadvantages. For example, software products for the automation of test runs and for the automatic optimisation of, say, engine operating conditions are, to a high degree, dependent on the reliability of the test run data. A setup that guarantees the plausibility of test results and detects non-permissible deviations early, significantly enhances the utility and economy of this software product.
Of course, methods for detecting error conditions are already known as, for example, from DE 198 41 260 A1 for error conditions in motor vehicles. With the aid of local diagnosis modules for partial systems of the vehicle, the function of said partial system is monitored and used for its control or for other partial systems. But measured values of the various partial systems are not checked at all, nor is their plausibility.
It is therefore necessary that the above-mentioned testing and measuring systems are equipped with a setup which, to the highest possible degree, can guarantee the usability of test results. The plausibility and quality of the measured results obtained have to be checked automatically and indicated to the user—not only after a test run has been carried out, i.e. when data is evaluated based on the recorded measured data, but as early as possible, preferably during the test run itself. An example of such a plausibility check, which in general can also be called a FDIC (Failure Detection, Isolation and Correction) method, is described in the EP 0 720 004 B1.
At present, such plausibility and measured data quality checking devices are only available in a very modest range and usually only relate to strictly defined and self-contained measuring instruments and measuring systems. It is known that some measuring instruments carry out a self test at the start of a test run and that, during the test run, certain function tests can be carried out on the measuring instruments. Some measuring systems also have calibration and diagnosis options that can be called up as required. There are also individually parametrisable monitoring options for, for example, critical values and the smoothness of individual measured signals. Thus, for example, a method is described in WO96/13764 where for an individual measured value a comparison is carried out with specific parameters of the measuring system itself as well as a second comparison with rules characteristic for the monitored system, and where the result of this check is weighted.
It is noteworthy, though, that for complex measuring tasks, e.g. on test stands in the vehicle industry, in particular on motor test benches, there are many measuring chains in existence. Depending on the test run aim, i.e. the conclusions to be drawn for the test piece from the test run, these individual measuring chains have differing relevance. The plausibility of an individual measured value, which has been ascertained by a FDIC method, for example, like the one described in the EP 0 720 004 B1, can have very different effects on the test run aim overall, which so far has not been taken into account in the commonly used methods. Particularly when performing test runs in the development and testing of complex equipment such as internal combustion engines, a clear evaluation of the reliability of measuring results is required in the interest of quality assurance, which goes beyond the plausibility of individual measured values. So far, the overall plausibility of a test run was generally examined by an experienced engineer who, on the one hand, could apply criteria from personal experience, but most of all consider correlations between measured data, based on techno-physical facts. Automated plausibility test systems capable of being adapted flexibly to the requirements of differing and complex testing and measuring systems, have not been created so far.
It is the object of the present invention, therefore, to provide a method by which a conclusion could be drawn about the value of plausibility nodes and their output in respect of a special measuring task. Thus, it is intended to provide a new generic approach based on a concept of general validity for evaluating measured data, in particular the evaluation of plausibility and quality of the measured and test data, an approach which allows the method to be carried out in consideration of the required, extensive test rules which in part are implemented in existing instruments and components of a measuring system, e.g. a test bench or also a mobile measuring instrument, and/or are provided in a software library. Furthermore, an additional object is a method with which it is possible to draw conclusions about the reliability of the test system results in relation to the desired measured values. As a further object, these methods should make the plausibility test system adaptable to the respective special task, i.e. the respective special test bench, the special measuring apparatus or similar and their actual configuration or, in terms of ‘plug & measure’, also largely be automatically adaptable.